1. Technical Field of the Invention
The invention relates generally to encoding and/or decoding of information; and, more particularly, it relates to segregation of portions of coded signal employed in accordance with such encoding and/or decoding.
2. Description of Related Art
As is known, many varieties of memory storage devices (e.g. disk drives), such as magnetic disk drives are used to provide data storage for a host device, either directly, or through a network such as a storage area network (SAN) or network attached storage (NAS). Typical host devices include stand alone computer systems such as a desktop or laptop computer, enterprise storage devices such as servers, storage arrays such as a redundant array of independent disks (RAID) arrays, storage routers, storage switches and storage directors, and other consumer devices such as video game systems and digital video recorders. These devices provide high storage capacity in a cost effective manner.
The structure and operation of hard disk drives is generally known. Hard disk drives include, generally, a case, a hard disk having magnetically alterable properties, and a read/write mechanism including Read/Write (RW) heads operable to write data to the hard disk by locally alerting the magnetic properties of the hard disk and to read data from the hard disk by reading local magnetic properties of the hard disk. The hard disk may include multiple platters, each platter being a planar disk.
As is known, many varieties of memory storage devices (e.g. disk drives), such as magnetic disk drives are used to provide data storage for a host device, either directly, or through a network such as a storage area network (SAN) or network attached storage (NAS). Typical host devices include stand alone computer systems such as a desktop or laptop computer, enterprise storage devices such as servers, storage arrays such as a redundant array of independent disks (RAID) arrays, storage routers, storage switches and storage directors, and other consumer devices such as video game systems and digital video recorders. These devices provide high storage capacity in a cost effective manner.
The structure and operation of hard disk drives is generally known. Hard disk drives include, generally, a case, a hard disk having magnetically alterable properties, and a read/write mechanism including Read/Write (RW) heads operable to write data to the hard disk by locally alerting the magnetic properties of the hard disk and to read data from the hard disk by reading local magnetic properties of the hard disk. The hard disk may include multiple platters, each platter being a planar disk.
All information stored on the hard disk is recorded in tracks, which are concentric circles organized on the surface of the platters. FIG. 1 depicts a pattern of radially-spaced concentric data tracks 12 within a disk 10. Data stored on the disks may be accessed by moving RW heads radially as driven by a head actuator to the radial location of the track containing the data. To efficiently and quickly access this data, fine control of RW hard positioning is required. The track-based organization of data on the hard disk(s) allows for easy access to any part of the disk, which is why hard disk drives are called “random access” storage devices.
Since each track typically holds many thousands of bytes of data, the tracks are further divided into smaller units called sectors. This reduces the amount of space wasted by small files. Each sector holds 512 bytes of user data, plus as many as a few dozen additional bytes used for internal drive control and for error detection and correction.
Within such hard disk drives (HDDs), error correction coding (ECC) is sometimes employed to ensure the ability to correct for errors of data that is written to and read from the storage media of a HDD. The ECC allows the ability to correct for those errors within the error correction capability of the code.
In disk drive controllers, disk drive modulation codes are often reverse-ordered (permuted) with the ECC system in order to eliminate the problem error propagation of large and efficient modulation code words, which could cause multiple ECC symbol corruption. Reversing the order of the modulation code encoder decoder (ENDEC) and the ECC system causes several issues that are difficult and costly to deal with in the hard disk drive controller. These disk drive controllers may be single-chip (SoC) or multi chip solutions. Reverse order ECC modulation may be performed to reduce error propagation. In multi chip solutions this may be achieved by moving.
Additionally RLL (Run Length Limiting) mode of the ENDEC is limits the run length of ones, zeros, or the two Nyquist (repeating “01” or “10”) patterns in the signal transmitted by the read channel within longitudinal recordings. The RDS (Running Digital Sum) mode for perpendicular recording limits the DC content of the signal. An RDS code will also suffice as an RLL code since controlling the DC content of a signal will always limit the run length. However, due to the rate of the RDS code, there is an unnecessary penalty for using it with a longitudinal recording channel. Hence, a nearly unity rate RLL code is provided. When an RLL or RDS encode is performed chronologically following the ECC encoding, the RLL/RDS decoding must be performed prior to the ECC decoding. For a system that performs the named operations in this order, there will be some degradation in the effectiveness of the ECC system due to error propagation. For this reason, the RLL/RDS ENDEC is also reverse ordered with the ECC.
With modulation codes, such as RLL/RDS, the redundant bits are only used for decoding purposes. (i.e., the redundant bits do not have any component of the user data embedded within them). However, encoding these redundant bits can result in decoding errors should an error be propagated within the encoding and decoding of these bits. Such an error may be propagated throughout the encoded data, corrupting the data beyond the capabilities of the ECC scheme.